The present invention relates to an improved apparatus which may be used as a manual operating apparatus or as a shaft locking apparatus with valves, chokes and other devices which have a remotely operated actuator including an axially moving stem or shaft to manually move the stem or shaft to one of its extreme positions and lock it in such position until the improved operator is released or manually moved to allow such movement.
Prior to the present invention, there have been many designs of manual operators or override mechanisms to be used with valves to move the valve stem against the force which is developed on the valve stem responsive to the fluid pressure which is present in the valve chamber and also against the force on the stem by a return spring, if one is used. U.S. Pat. No. 4,844,407 is an example of such prior manual operator and override mechanisms.
U.S. Pat. No. 4,194,718 Baker et al is an example of the prior art of such override mechanisms as applied to a choke and which can be operated by a handwheel. It includes means for releasably connecting the manual operator to the gate to manually move the gate and for releasing the manual operator from the gate to allow such movement.
U.S. Pat. No. 3,378,224 to Boyle discloses a gate valve which is piston actuated together with a handwheel having a sleeve threaded on the shaft which extends through the piston. Rotation of the handwheel causes movement of both the piston and the valve member.
U.S. Pat. No. 4,189,980 discloses a manual control apparatus which has a split drive nut and a camming system which coacts with the rotation system for bringing the split drive nut into engagement with the threaded drive screw and rotating the split nut to move the drive screw and the valve member connected thereto.
U.S. Pat. No. 3,628,397 discloses a valve member having a ball nut secured to the upper portion of the piston and a ball shaft secured to the top of the bonnet and mounted so that its rotation causes movement of the piston and valve member. During normal operation, movement of the piston will cause rotation of the ball shaft.
U.S. Pat. No. 4,213,480 discloses an override mechanism for a valve in which a nut is threaded onto the drive stem and is engaged by a drive sleeve which telescopes onto the nut and splines connect the sleeve to the nut. Rotation of the sleeve rotates the nut which contacts one of the abutment surfaces and then causes movement of the gate.
The prior devices have had the problem of being difficult to turn in both directions when the valve chamber is pressurized. At times the force of such pressure is sufficient to allow unlocking or opening without releasing the fluid pressure to which the stem is exposed.